The present invention generally related to an active signal modification circuit with a common mode bypass for use with multi-mode signals conveyed within a combination signal of low frequency and high frequency components.
In the past, passive signal conditioning systems have been proposed for use with cable assemblies that convey data signals, power, speech signals and the like. Existing passive signal conditioning systems typically operate with two signal lines, along which a passive equalization circuit is provided. FIG. 1 illustrates an exemplary conventional system having a passive equalization circuit 10 connected with two input lines 12 and 14 and two output lines 16 and 18. The input lines 12 and 14 convey a differential mode signal overlapped with a common mode signal. The term “common mode” as used throughout shall refer to a signal conveyed over one or more input lines, where the signal changes level on each input line at substantially the same time and by substantially the same amount. The term “differential mode” as used throughout shall refer to signals being conveyed over a pair of lines, where the signals may change levels at different times and by different amounts. The passive equalization circuit 10 may perform equalization or filtering upon one or both of the differential and common mode signals.
However, conventional passive equalization circuits have experienced certain disadvantages. As cable assemblies increase in length, the signals conveyed by these cable assemblies become more and more attenuated. The need has arisen to add active components to the cable assembly in order to amplify, filter, modify or otherwise enhance the signals conveyed by the cable assembly. Active components that amplify or boost the signals typically amplify a difference between the input signals. Active components that operate based on a difference between the input lines also function as common mode reject filters to block passage of any signal that is common to both input lines.
Hence, cable assemblies that include active amplification components heretofore, were unable to convey both differential mode and common mode signals since the amplifiers blocked any common mode signal component provided on the input lines.
A need remains for an improved active signal modification circuit capable of transmitting both common mode and differential mode signals.